(1) Field of the Invention
This invention relates to oscillation type flying shears, and more particularly it is concerned with an oscillation type flying shear suitable for use in shearing material to specified lengths by repeatedly starting and shutting down the shear.
(2) Description of the Prior Art
In oscillation type flying shears, it is required to make the cutter velocity match the velocity of material to be sheared in order to avoid any damage to the material to be sheared that might otherwise occur. However, since the cutting blade horizontal velocity V.sub.s undergoes changes as a cosine function of the rotational angle .omega..sub.t of the main crank shaft as indicated by the equation set forth below, it is impossible to make the cutting blade horizontal velocity V.sub.s match the velocity V.sub.m of the material to be sheared at all times during a shearing operation. EQU V.sub.s =.pi.DN.sub.s cos .omega.t (1)
where
N.sub.s V.sub.m /L PA1 N.sub.s : revolution of main crank shaft. PA1 L: shearing length. PA1 D: amplitude of oscillation of cutting blade. PA1 t.sub.m : Actual thickness of material.
Assume that the two velocities do not match when shearing is initiated or when the cutting blades bite into the material to be sheared. Then scratches would be caused by the cutting blade on the material to be sheared. On the other hand, if there are great differences between the cutting blade velocity and the peripheral velocity of means for moving the material to the shear, such as a pinch roller, after the cutting blades have bitten into the material, abrasions would be caused on the material by rubbing. Of these two injuries to the material to be sheared, scratches are of greater concern because they are caused by a sharp edge and larger in extent. Thus, since scratches causes greater trouble, it is usual practice to effect adjustments in such a manner that the cutting blade horizontal velocity matches the velocity of the material to be sheared in the position in which the cutting blades bite into the material.
In order to absorb shock and reduce the shearing force when shearing is carried out, it is also practiced to provide either the upper cutting blade or the lower cutting blade with a rake angle .alpha. as shown in FIG. 1 (wherein no upper cutting blade is shown). Thus when the upper and lower cutting blades are both in contact with the material 1 to be sheared, the spacing between them is varied not only by the thickness of the material 1 but also by the width thereof. If the change in the spacing between the upper and lower cutting blade that occurs from the time the cutting blades come into contact with the material 1 until the time shearing is completed is indicated as an equilibrium thickness T, then T can be expressed as follows: ##EQU1## where B: Width of material.
Thus, in oscillation type flying shears, it is necessary that the cutting blade horizontal velocity be adjusted in accordance with the equilibrium thickness of the material to be sheared in such a manner that the cutting blade horizontal velocity matches the velocity of the material to be sheared when the cutting blade bites into the material.
There are two types of oscillation type flying shears for shearing material to specified lengths. One type is continuously operated, and the other type is repeatedly started and shut down.
In the former type of shear, there is provided means for bringing the cutting blade velocity into synchronism with the velocity of the material to be sheared at the time the cutting blade bites into the material, by varying the amplitude of oscillation of the cutting blade. This synchronizing means is complex in construction and unable to have its size reduced because of the need to have substantial strength. Thus it is impossible to reduce the amplitude of oscillation of the cutting blade and hence to reduce a minimum shearing length and to increase the changes in shearing length.
The latter type of shear includes a shear disclosed in Japanese Patent Laid-Open Publication No. 72281/78 which offers the advantage that, since the shear is capable of keeping constant the amplitude of oscillation of the cutter, the oscillating means can be reduced in size and the shearing length can be varied over a wide range of values by merely changing the interval between starting of the shear and shutting down thereof. However, the shear has the disadvantage that difficulties are encountered in adjusting the cutting blade velocity. More specifically, in the shear disclosed in the laid-open patent publication referred to hereinabove, oscillating motion is sustained by transmitting the rotation of a main crank shaft to an oscillating crank via gearing and by transmitting the eccentric rotational movement of the oscillating crank to a frame via a link. In this shear, adjustments of the frame velocity or cutting blade velocity are effected by varying the position in which the link is attached to the frame. Stated differently, the part to be adjusted is located in the frame which moves in oscillating movement and consequently no adjustments can be effected during a shearing operation. An added disadvantage is that the part to be adjusted is located in a small space between the gearing and the frame, thereby making the adjusting operation low in efficiency.